Acute kidney injury (AKI) is a significant factor predisposing chronic kidney disease (CKD), however the factors mediating CKD progression are not clear. Work from the previous project period identified T-helper 17 cells (Th-17) as a primary lymphocyte population activated by AKI and further demonstrated that it is strongly activated by exposure of post AKI rats to high salt diet. Recent preliminary data indicate a potential role for altered lymphocyte intracellular calcium signaling in mediating enhanced IL17 activity. The overarching hypothesis to be tested is that AKI results in persistent IL-17 activity from CD4+ cells and this activity is integral to the subsequent development of CKD. As such, Specific aim 1 of this application will investigate the role of Th-17 cells in the mediation of the AKI to CKD transition in rats. The studies will utilize a rat model of AKI-to CKD established in our laboratory. Two approaches will be used to inhibit Th17 activity. In one series of studies, we will use an antibody-based approach to block IL17 activity in rats in vivo. Additional studies will utilize a transgenic rat in which the ROR?T gene has been mutated. This rat shows impaired activation of Th-17 cells following AKI and lymphocytes obtained from these rats show an impaired IL17 responses in vitro. Using either approach we will test whether Th17 cells activated by elevated dietary salt following recovery from AKI participate in the processes of renal fibrosis, sodium sensitive hypertension, altered vascular reactivity and distant organ injury following AKI Specific aim 2 of this application will more precisely examine altered lymphocyte signaling associated with IL17. Isolated lymphocytes from normal or post AKI rats will be stimulated in vitro (by elevated Na+ and Ang II) for enhanced IL17 synthesis. The goal of these studies will be to determine how prolonged enhanced IL17 responses to are retained in CD4 cells following resolution of renal injury. We will also investigate potential physiologically relevant mediators that may activate these responses in vivo. Additional studies in this aim will investigate contribution of the store-operated Ca++ Oria1 to altered Ca signaling and the IL17 response. Finally studies in this aim will seek to investigate the effect of in vivo inhibition of Oria-1 on the activation of Th-17 cells and the AKI to CKD transition. Specific aim 3 will determine whether activation of Th17 cells may underlie the AKI to CKD transition in human patients. These studies will utilize samples available from the ASSESS-AKI consortium which has collected samples from AKI patients for up to 4 years following hospital discharge. We will compare circulating Th17 cytokines as an initial step to determine the activity of this pathway in patients with AKI who progress versus patients who recovery renal function as well as control patients.